ANSWER
[tex]y = 4[/tex]
EXPLANATION
Since the y-coordinate of all the points on a given line is 4, it means the line is parallel to the x-axis and has slope, zero.
The equation of all lines parallel to the x-axis that pass through:
[tex](x_1,y_1)[/tex]
is
[tex]y = y_1[/tex]
Since the line passes through
[tex](x_1,4)[/tex]
or
(0,4)
Its equation is:
[tex]y = 4[/tex]
See attachment for graph.